Plastics have found ever increasing use as replacements for glass and metal containers in packaging, especially of foods and beverages. The advantages of such plastic packaging includes lighter weight, decreased breakage (versus glass) and potentially lower costs. However, the gas-barrier properties of common packaging plastics, such as polyolefins, e.g., polyethylene and polypropylene, and polycarbonates, present major disadvantages in the packaging of many foods and beverages. For example, many foods and beverages are sensitive to oxidation and must be protected from oxygen to prevent discoloration or other detrimental effects. Further, plastic beverage containers suffer comparative shelf-life problems versus glass or metal due to the loss of carbon dioxide through the plastic container.
Numerous barrier coatings have been developed including, e.g., barrier materials based on vinylidene chloride or on ethylene-vinyl alcohol. Each of these materials have drawbacks. Ethylene-vinyl alcohol-based polymers lose barrier properties upon exposure to water and packages of this material cannot generally undergo retort, i.e., heating under pressurized steam for pasteurization. Vinylidene chloride-based polymers have been recognized as having excellent gas-barrier properties, but preparation of such vinylidene chloride-based polymers must generally be done under high pressure. Further, since vinylidene chloride-based barrier materials include halogen atoms, the disposal of such materials via incineration poses environmental problems. In addition, both vinylidene chloride-based polymers and ethylene-vinyl alcohol based polymers exhibit loss of adhesion after undergoing retort.